Oxazolidinone structures-containing prepolymeric epoxy mixture

ABSTRACT

In a process for producing a prepolymer epoxy resin mixture with oxazolidinone structures, an insoluble reaction resin powder which has no isocyanate groups and consists of an epoxy resin mixture containing a reaction accelerator and filler and having isocyanurate structures, is fed to a continuously working reactor and reacted at temperatures up to 200° C., with reactor temperature at 140°-190° C., and then the extruded material is cooled down to a temperature of &lt;50° C. with the aid of a cooling device mounted at the outlet die of the reactor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for making an oxazolidinonestructures-containing prepolymeric epoxy resin mixture and to anapparatus for carrying out said process.

2. Description of Related Art

It is known from WO 90/15089 that epoxide-terminated polyoxazolidinones(in that document referred to simply as polyoxazolidones) can beprepared by reaction of a polyepoxide and a polyisocyanate at elevatedtemperature in the presence of a catalyst. To this end, from 5 to 30 wt% of the polyisocyanate is added within 30 to 90 min to a mixture of 70to 95 wt % of the polyepoxide and 0.01 to 2 wt % of the catalyst, andthe resulting reaction mixture is then heated at a temperature of 110°to 200° C. for a period of 5 to 180 minutes. By regulating variousprocess parameters, the process is carried out so that in the resultingepoxy-terminated polyoxazolidinone, which is also referred to asisocyanate-modified epoxy resin, 50 to 100% of the original isocyanategroups are converted into oxazolidinone rings and 0 to 50% intoisocyanurate rings.

In the known process, the polyepoxide is, in particular, bisphenol A ortetrabromobisphenol A, and the polyisocyanate is4,4'-methylene-bis(phenyl isocyanate) (MDI) or an isomer thereof,polymeric MDI or toluylene diisocyanate. A suitable catalyst (for thereaction of the polyepoxide and the polyisocyanate) is, in particular,an imidazole or tetraphenylphosphonium bromide. The catalystconcentration is preferably from 0.02 to 1 wt %, particularly 0.02 to0.1 wt %, based on the total weight of the polyepoxide and thepolyisocyanate. To prepare the polyoxazolidinones, the catalyst,optionally dissolved in a suitable solvent, is added to the polyepoxide,in general at a temperature below the reaction temperature of 110° to200° C. The temperature is then raised to the reaction temperature andkept at this level while adding the polyisocyanate under controlledconditions, namely dropwise.

A similar process, known from EP 0 296 450 A1, is used for makingoxazolidinone groups--(in that document referred to simply asoxazolidone groups) containing oligomeric polyepoxides from bisepoxidesand diisocyanates. By this process, either a bisepoxy ether with OHgroups corresponding to a hydroxyl number of at least 2 is made to reactwith an aromatic diisocyanate containing two NCO groups of differentreactivity in an amount of at least 1/4 of the weight of thediisocyanate, or a bisepoxy ester with OH groups corresponding to ahydroxyl number of at least 2 is made to react with an aromatic,aliphatic or cycloaliphatic diisocyanate in a weight ratio of NCO groupsto epoxide groups of 1:1.4 to 1:2.5--both reactions being carried out inthe presence of a phosphonium salt as catalyst at 140° to 180° C. Thecatalyst is used in an amount of 0.005 to 1.0 wt %, preferably 0.01 to0.5 wt %, based on the bisepoxide.

In this process, it is essential that the oxazolidinone epoxy resins areobtained only when 0H groups-containing epoxy resins are made to reactwith diisocyanates containing NCO groups of different reactivity, in thepresence of a phosphonium salt as catalyst at about 160° C. To preparethe polyepoxide, the bisepoxy resin and the catalyst are heated to 160°C. under nitrogen. The diisocyanate is then added dropwise to the meltat a rate such that a temperature of about 170° C. is maintained. Afterall the diisocyanate has been added, the mixture is allowed to agitateat 160° C. until the calculated epoxide content has been reached andreactive NCO can no longer be detected.

Both known processes have been described only for laboratory batchsizes. It is essential in this respect that the polyisocyanate be addeddropwise to the catalyst-containing polyepoxide. Hence, it is hardlypossible to carry out the described processes economically on anindustrial scale. Moreover, by these processes only filler-free reactionresin mixtures can be used.

SUMMARY OF THE INVENTION

The object of the invention is to provide an industrial process formaking an oxazolidinone structures-containing prepolymeric epoxy resinmixture that is storage-stable, soluble or fusible, latently reactiveand curable.

According to the invention, this objective is reached by feeding to acontinuous reactor an isocyanate groups-free, insoluble, powderyreaction resin consisting of an isocyanurate structures-containing epoxyresin mixture containing a catalyst and a filler, causing said resin toreact at a reaction temperature of up to 200° C., the reactortemperature being from 140° to 190° C., and cooling the extrudate to atemperature of <50° C. with a cooling device located at the outlet dieof the reactor.

DETAILED DESCRIPTION OF THE INVENTION

A suitable continuously operating reactor for the process according tothe invention is, in particular, a twin-screw extruder. Advantageously,the ratio of the screw length to the outside screw diameter of theextruder is from 20 to 50 and particularly from 25 to 40. Moreover, theextruder is preferably designed so that the residence time of thematerial at a screw speed of >10 rpm is less than 5 min, preferably lessthan 3 min. and so that axial backflow is minimized.

The insoluble, isocyanate groups-free, powdery reaction resin can be fedto the twin-screw extruder by means of a twin-screw metering device, forexample at a rate of 150 g/min. The extruder contains conveying screwelements (screw diameter, for example: 31.8 mm, screw length: 880 mm)and is provided with five thermostattable barrel zones heated, forexample, at 160° C. At a screw speed of 90 rpm, the residence time ofthe material is, for example, <1 minute. The extrudate emerging througha slot die passes over a cooled slide-off ramp and is rapidly cooled toa temperature below 50° C., which causes the epoxy resin mixture tosolidify into continuous ribbon-shaped strips. On a take-off belt, thesestrips are pulled under a counter-roll and thus coarsely comminuted. Thepre-comminuted product is ground to the desired particle size in animpact mill. The free-flowing, storage-stable, soluble or fusible,latently reactive, oxazolidinone structures-containing prepolymericepoxy resin mixture is stored with exclusion of moisture.

The process according to the invention involves the use of an insoluble,isocyanate groups-free, powdery reaction resin. Said powdery reactionresin is prepared from a filler-containing, heat-polymerizable reactionresin mixture of polyepoxy resin and polyisocyanate resin with a molarratio of epoxide groups to isocyanate groups of >1, preferably 1.5 to4.0. The polyepoxy resin is a mixture of di- and polyfunctional epoxyresins, the ratio of polyfunctional to difunctional epoxy resin beingfrom 0.1 to 1.7 and preferably from 0.2 to 0.75, based on epoxidegroups. The reaction resin mixture of polyepoxide and polyisocyanateresin is made to react at a temperature of up to 180° C. in the presenceof a substituted imidazole as catalyst, said imidazole being used in anamount of 0.5 to 2.5%, based on the polyepoxy resin.

Whereas according to the prior art, as indicated in particular by thepractical examples of said prior art, low catalyst concentrations areused, namely from 0.01 to 0.35% (WO 90/15089) or 0.1% (EP 0 296 450 A1),in both cases based on the polyepoxide, substantially higher amounts ofcatalyst are needed to prepare reactive, curable prepolymeric epoxyresin mixtures. Hence, in the process according to the invention, thecatalyst concentration is from 0.5 to 2.5% (by weight), preferably from1.0 to 1.8%, based on the mixture of di- and polyfunctional epoxyresins. Such high catalyst concentrations are required to ensure thecuring of the latently reactive prepolymeric epoxy resin mixture withinan industrially relevant time without post-catalysis--which forfiller-containing systems is expensive.

On a pilot-plant scale, the isocyanate groups-free, insoluble powderyreaction resin is advantageously prepared in a mixing vessel, preferablyin a vertical kneader, a continuous reactor being used for largeramounts of material. The preparation and processing of the reactionresin mixture in a vertical kneader is carried out as follows. The di-and polyfunctional epoxy resins and the polyisocyanate resin are chargedto the vertical kneader which is equipped with a thermostattable andevacuable kneading trough and with kneading blades and permitscontinuous measurement of the temperature of the reaction resin mixture.The mixture is heated to a temperature of up to 100° C., blended bymixing (i.e. agitation) and degassed. The filler and optionally otheradditives are then added in portions to the heated reaction resinmixture, and the mixture is degassed for at least 1 hr at reducedpressure and at a temperature of up to 100° C. with continuing mixing.The catalyst is then blended in, and the temperature of the mixingvessel is adjusted to 160°-180° C. The conversion of the reaction resinmixture into the powdery reaction resin occurs at reaction temperaturesabove 130° C. usually within a few minutes, while the steady mixing inthe mixing vessel produces a free-flowing product. To discontinue thereaction, the temperature of the mixing vessel is rapidly reduced bymeans of a cooling thermostat, and the powdery reaction resin is broughtto a temperature below 50° C. with mixing. The epoxide group conversionrequired at the time the reaction is discontinued is determined inpreliminary tests. The absence of isocyanate groups in the powderyreaction resin is established by IR spectrophotometry. Before use, thefree-flowing, storage-stable, insoluble powdery reaction resin obtainedin this manner can be stored with exclusion of moisture for longperiods, as needed.

When a continuous reactor is used to prepare the isocyanate groups-free,insoluble powdery reaction resin, the resin mixture can be prepared andfed to the reactor in different ways. In one case--to prepare a resincomponent--the di- and polyfunctional epoxy resins, the polyisocyanateresin and the filler are degassed in a thermostattable and evacuablemixing vessel at a temperature of up to 100° C. with mixing. In a secondmixing vessel the catalyst component is prepared by dissolving ordispersing the catalyst in one of the resin components of theformulation or in part thereof, with degassing. The two components arethen fed to a static mixing tube, and the reaction resin mixture beingdischarged from the mixing tube is metered into a reactor.

In another case, the resin component is prepared as in the first case.The catalyst component is prepared by vigorously blending the catalystwith part of the filler used in the formulation. The two components arethen fed into a twin-screw extruder, for example by means of aperistaltic pump or a twin-screw powder metering device. In contrast tothe twin-screw extruder described hereinabove, the extruder used for thepreparation of the insoluble powdery reaction resin contains bothconveying screw elements and kneading elements and has a greater numberof thermostattable barrel zones.

The reaction of the resin component with the catalyst component to givethe isocyanate groups-free, insoluble reaction resin powder ispreferably carried out at a lower temperature than the reaction of thereaction resin powder to form the prepolymeric epoxy resin mixture. Thestorage-stable, free-flowing reaction resin powder can be metered intothe continuous reactor in simple fashion without expensive meteringsystems. Thus, for example for product optimization, free-flowingmixtures of reaction resin powders of different composition or mixtureswith fillers and/or other additives can be introduced into and processedin the continuous reactor inexpensively.

To prepare the insoluble powdery reaction resin, a polyepoxy resinmixture, namely a mixture of di- and polyfunctional epoxy resins isused, as previously indicated. Suitable epoxy resins are, in particular,bisphenol A and bisphenol F epoxy resins and phenol novolak and cresolnovolak epoxy resins or silicone epoxy resins, triglycidyl isocyanurate,tetra-glycidyldiaminodiphenylmethane and polyglycidylphosphorus resins.Particularly suitable silicone epoxy resins are those having thefollowing structure: ##STR1## wherein n is an integer from 0 to 25,

x is an integer from 0 to 3,

R=alkyl or aryl,

Q=--(CH₂)₃ SiR₂ O(SiR₂ O)_(n) SiR₂ R¹,

n and R having the afore-indicated meaning and R¹ denoting a groupbearing epoxy functionality and having 6 carbon atoms.

The silicone epoxy resin is used in an amount of up to 20%, preferably 1to 7%, based on the filler-free reaction resin mixture of polyepoxyresin and polyisocyanate resin.

Preferred polyisocyanate resins are isomer mixtures of diphenylmethanediisocyanate. Also suitable are, for example, toluylene diisocyanateisomer mixtures and prepolymers of diphenylmethane diisocyanate isomermixtures. Mixtures of said polyisocyanate resins can also be used.

Substituted imidazoles are used as catalysts (i.e. reactionaccelerators) for the process of the invention. Preferred are2-ethyl-4-methylimidazole, 2-phenylimidazole and1-cyanoethyl-2-phenylimidazole. Other suitable catalysts are, forexample, 1,2-dimethylimidazole, 1-cyanoethyl-2-methyl-imidazole,2-isopropylimidazole and 1-benzyl-2-phenyl-imidazole. The catalyst isused in amount of 0.5 to 2.5%, preferably 1.0 to 1.8%, based on thepolyepoxy resin, namely on the mixture of the di- and polyfunctionalepoxy resins.

Suitable fillers are, in particular, mineral fillers, such as fusedquartz with angular (i.e. splintery) and/or spherical particles (ofvarying particle size distribution). Moreover, ceramic fillers such asaluminum oxide and mixtures of ceramic and mineral fillers can be used.Fibrous fillers, such as short glass fibers, are also suitable.

The composition of the reaction resin mixture of polyepoxy resin andpolyisocyanate resin used in the process according to the inventiondiffers markedly from that of the reaction mixtures used according tothe prior art. In fact, to prepare the reaction resin mixture, mixturesof di- and polyfunctional epoxy resins are used, namely mixtures ofepoxy resins of different chemical structure and differentfunctionality. Such mixtures, however, are not known from the prior art.Moreover, neither the particularly well suited catalyst1-cyanoethyl-2-phenylimidazole nor the silicone epoxy resins of theindicated type which are important for the processing properties nor thetetraglycidyldiaminodiphenylmethane, which is particularly advantageousfor raising the glass transition temperature, are mentioned in the priorart.

The preparation of free-flowing, storage stable, isocyanate groups-free,isocyanurate structures-containing powdery reaction resins obtained froma mixture of a di- and a polyfunctional epoxy resin and a polyisocyanateresin in a molar ratio of epoxide groups to isocyanate groups of >1 byuse of a substituted imidazole as catalyst has thus far not beendescribed. What is known is the preparation of filler andcatalyst-containing resin mixtures from epoxy and isocyanate resins thatare solid at room temperature by use of an imidazole. In this case, thecomponents are mixed by kneading at 80° C. (see: JP-OS [Japaneseunexamined patent application] 50-059499 and JP-OS 51-128400). Thesecatalyst-containing resin mixtures are molded and cured at a temperatureof up 180° C. Such processes, in contrast to the process according tothe invention, do not give isocyanate groups-free, insoluble powderyreaction resins, but, rather, fusible resin mixtures that are processedby molding.

Those skilled in the art could not have predicted the possibility ofpreparing a soluble or fusible prepolymeric epoxy resin mixture from theinsoluble, isocyanate groups-free (chemically crosslinked) powderyreaction resins by reaction extrusion according to the process of theinvention. Surprisingly, the polyfunctional epoxy resins such as saidsilicone epoxy resins and tetraglycidyldiaminodiphenylmethane containedin the powdery reaction resin and the use of a high catalystconcentration at a temperature of up to 200° C. do not cause furthercuring of the powdery reaction resin, but result in a storage-stable,soluble or fusible, curable epoxy resin mixture which can be curedwithout post-catalysis, which for filler-containing reaction resinswould be expensive.

The invention will be illustrated in greater detail by the followingexamples.

EXAMPLE 1 Preparation of an Isocyanate Groups-free Insoluble PowderyReaction Resin

To a vertical kneader were charged 1530 g of bisphenol A epoxy resin(epoxide content: 5.78 mol/kg), 99 g of a silicone epoxide (epoxycontent: 1.9 mol/kg) prepared as described in Example 9 of EuropeanUnexamined Patent Application EP-OS 0 399 199, 495 g oftetraglycidyldiaminodiphenylmethane (epoxide content: 8.2 mol/kg) and360 g of a diphenylmethane diisocyanate isomer mixture (isocyanatecontent: 7.9 mol/kg), and the mixture was heated to 80° C. with mixing.To this mixture were then added in portions and with mixing 4347 g ofspherical fused quartz, 1863 g of angular fused quartz and 90 g ofcarbon black. The mixture was degassed at 80° C. for 1 hr with mixing.Then 3.3 g of 1-cyanoethyl-2-phenylimidazole was added to the reactionresin mixture, and the mixture was degassed for 10 min with mixing. Thetemperature of the mixing vessel was then adjusted to 160° C., and thereaction resin mixture was heated with mixing. The reaction resulting inthe powdery reaction resin started at about 130° C. The course of thereaction was followed continuously by temperature measurement. Thereaction was discontinued 1 min after the reaction resin mixture hadsolidified. This was done by cooling the mixing vessel with the aid of acooling thermostat. The temperature of the reaction resin was thenreduced to below 50° C. with continuing mixing. Continuing mixingproduced the insoluble reaction resin as a free-flowing, storage-stablepowder (epoxide content: 1.28 mol/kg). As indicated by IRspectrophotometry, this product was devoid of isocyanate groups.

EXAMPLE 2 Preparation of an Oxazolidinone Structures-containingPrepolymeric Epoxy Resin Mixture

By means of a powder-metering device, the isocyanate groups-free,insoluble powdery reaction resin prepared as described in Example 1 wasfed to a co-currently rotating twin-screw extruder (screw length: 880mm, outside screw diameter: 31.8 mm) at a constant rate of 30 g/minute.The extruder screws were provided exclusively with conveying elements.The five barrel zones of the extruder were set at 160° C. Thetemperatures in the individual barrel zones were as follows: zone 1:152° C., zone 2: 158° C., zone 3: 160° C., zone 4: 160° C., zone 5: 155°C. The screw speed was 90 rpm and the residence time of the material inthe extruder was 1.0 minute. The extrudate was removed through a doubleslot die (cross-section: 2 mm×2 mm each), cooled to a temperature below50° C. by means of a cooled take-off ramp and then coarsely comminutedon an attached elastic haul-off belt by means of a counter-roll. Thepre-comminuted extrudate was ground to the desired particle size in animpact mill. The resulting free-flowing, latently reactive, curableprepolymeric epoxy resin mixture (epoxide content: 0.86 mol/kg); meltingrange: 75°-95° C.) was stored at room temperature with exclusion ofmoisture.

EXAMPLE 3 Preparation of an Isocyanate Groups-free Insoluble PowderyReaction Resin

To a vertical kneader were charged 825.2 g of bisphenol A epoxy resin(epoxide content: 5.78 mol/kg), 50.1 g of a silicone epoxide (epoxidecontent: 1.9 mol/kg) prepared as described in Example 9 of EP-OS 0 399199, 262.1 g of tetraglycidyldiaminodiphenylmethane (epoxide content:8.2 mol/kg) and 286.4 g of a diphenylmethane diisocyanate isomer mixture(isocyanate content: 7.9 mol/kg), and the mixture was heated to 85° C.with mixing. To this mixture was added in portions 7560 g of aluminumoxide (particle size<150 μm) and the mixture was degassed 1 hr at 85° C.To the reaction resin mixture was added 16.2 g of 2-phenylimidazole, andthe mixture was degassed 10 min with mixing. The reaction resin mixturewas then worked up as in Example 1. This gave an isocyanate groups-free,insoluble reaction resin in the form of a free-flowing powder (epoxidecontent: 0.7 mol/kg).

EXAMPLE 4 Preparation of an Oxazolidinone Structures-containingPrepolymeric Epoxy Resin Mixture

By means of a powder-metering device, the isocyanate groups-free,insoluble powdery reaction resin prepared as described in Example 3 wasadded to a twin-screw extruder described in Example 2 at a constant rateof 60 g/minute. The five barrel zones of the extruder were set at 165°C. The temperatures in the individual barrel zones were as follows: zone1: 155° C., zone 2: 162° C., zone 3: 165° C., zone 4: 165° C., zone 5:159° C. The screw speed was 95 rpm and the residence time of thematerial in the extruder was 0.9 minute. Work-up as in Example 2 gave afree-flowing, latently reactive, curable prepolymeric epoxy resinmixture (epoxide content: 0.49 mol/kg; melting range: 75°-95° C.) whichwas stored at room temperature with exclusion of moisture.

EXAMPLE 5 Preparation of an Isocyanate Groups-free, Insoluble, PowderyReaction Resin

To prepare a resin component, 2550 g of bisphenol A epoxy resin (epoxidecontent: 5.78 mol/kg), 155 g of a silicone epoxide (epoxide content: 1.9mol/kg) prepared as described in Example 9 of EP-OS 0 399 199, 810 g oftetraglycidyldiaminodiphenylmethane (epoxide content: 8.2 mol/kg) and885 g of an isomer mixture of diphenylmethane diisocyanate (isocyanatecontent: 7.9 mol/kg) were charged to a thermostattable and evacuablemixing vessel (effective capacity: 20 l) and the mixture was heated to60° C. with mixing. To this mixture were added in portions 6195 g ofspherical fused silica, 2655 g of angular fused silica and 135 g ofcarbon black, and the mixture was degassed 1 hr at 60° C. with mixing.To prepare a catalyst component, 1050 g of spherical fused silica, 450 gof angular fused silica, 15 g of carbon black and 55.5 g of1-cyanoethyl-2-phenylimidazole were uniformly mixed. The resin componentwas added to a twin-screw extruder by means of a peristaltic pump at asteady rate of 42 g/min, and the catalyst component was added to atwin-screw extruder by means of a twin-screw metering device at aconstant rate of 5 g/minute The twin-screw extruder was extended by amixing section located ahead of the processing section and by adischarge section downstream of the processing section. The extrudatewas removed from the extruder without using an extrusion die. The screwlength was 1232 mm and the outside screw diameter was 31.8 mm. Thescrews of the extruder were built as follows. The feeding zone containedconveying screw elements, the adjacent mixing zone contained kneadingelements, the processing zone contained conveying screw elements and theend of the screw was once again provided with kneading elements for thepurpose of comminuting the extrudate to a uniform particle size and toremove it from the open extruder. The seven barrel zones of the extruderwere set at the following temperatures: zone 1 (blending zone): 62° C.,zone 2: 110° C., zones 3 to 7: 150° C. The screw speed was 80 rpm andthe residence time of the material in the twin-screw extruder was 1.3minutes. The extrudate was cooled to 40° C. by means of a cooledtake-off ramp. The resulting isocyanate groups-free, insoluble, powderyreaction resin (epoxide content: 1.38 mol/kg) was stored at roomtemperature.

EXAMPLE 6 Preparation of an Oxazolidinone Groups-containing PrepolymericEpoxy Resin Mixture

By means of a powder-metering device, the isocyanate groups-free,insoluble, powdery reaction resin prepared in Example 5 was fed to atwin-screw extruder described in Example 2 at a constant rate of 150g/minute. The five barrel zones of the extruder were set at 170° C. Thetemperatures in the individual barrel zones were as follows: zone 1:162° C., zone 2: 166° C., zone 3: 170° C., zone 4: 170° C., zone 5: 163°C. The screw speed was 100 rpm and the residence time of the material inthe extruder was 0.8 minute. Work-up as in Example 2 gave afree-flowing, latently reactive, curable prepolymeric epoxy resinmixture (epoxide content: 0.84 mol/kg; melting range: 75°-95° C.) whichwas stored at room temperature with exclusion of moisture.

We claim:
 1. A process for continuously producing anoxazolidinone-containing epoxy resin prepolymer mixture, comprising thesteps of: feeding an isocyanate group-free, powdery reaction resincomprising an isocyanurate-containing epoxy resin prepolymer mixturecontaining an inertly substituted imidazole as a catalyst, in an amountof 0.5 to 2.5% by weight based on the epoxy resin, and containing afiller, to a continuously working reactor; reacting the resin at areaction temperature of up to 200° C., the reactor temperature beingfrom 140° to 190° C.; and continuously cooling extrudate emerging froman outlet die of the reactor to a temperature of <50° C. by means of acooling device located at the outlet die of the reactor.
 2. The processaccording to claim 1 wherein the powdery reaction resin is prepared froma thermally-polymerizable filler-containing reaction resin mixture of apolyepoxy resin comprising a mixture of di- and polyfunctional epoxyresins and a polyisocyanate and having a molar ratio of epoxide groupsto isocyanate groups of >1 at a temperature of up to 180° C. by usingthe inertly substituted imidazole catalyst.
 3. The process according toclaim 2 wherein the powdery reaction resin is prepared in a kneader orin a continuous reactor.
 4. The process according to claim 1 wherein theepoxy resin is selected from the group consisting of a bisphenol A epoxyresin, a bisphenol F epoxy resin, a phenol novolak epoxy resin, a cresolnovolak epoxy resin, a silicone epoxy resin, triglycidyl isocyanurate,tetraglycidyldiaminodiphenylmethane and a polyglycidylphosphorus resin.5. The process according to claim 2 wherein the epoxy resin is selectedfrom the group consisting of a bisphenol A epoxy resin, a bisphenol Fepoxy resin, a phenol novolak epoxy resin, a cresol novolak epoxy resin,a silicone epoxy resin, triglycidyl isocyanurate,tetraglycidyldiaminodiphenylmethane and a polyglycidylphosphorus resin.6. The process according to claim 3 wherein the epoxy resin is selectedfrom the group consisting of a bisphenol A epoxy resin, a bisphenol Fepoxy resin, a phenol novolak epoxy resin, a cresol novolak epoxy resin,a silicone epoxy resin, triglycidyl isocyanurate,tetraglycidyldiaminodiphenylmethane and a polyglycidylphosphorus resin.7. The process according to claim 2 wherein in the epoxy resin mixturethe molar ratio of polyfunctional to difunctional epoxy resin is 0.2 to0.75, based on the epoxide groups.
 8. The process according to claim 5wherein in the epoxy resin mixture the molar ratio of polyfunctional todifunctional epoxy resin is 0.2 to 0.75, based on the epoxide groups. 9.The process according to claim 2 wherein the polyisocyanate is an isomermixture of diphenylmethane diisocyanate or of toluylene diisocyanate ora prepolymer of a diphenylmethane diisocyanate isomer mixture.
 10. Theprocess according to claim 1 wherein the catalyst is2-ethyl-4-methylimidazole, 2-phenylimidazole or1-cyanoethyl-2-phenylimidazole.
 11. The process according to claim 2wherein the catalyst is 2-ethyl-4-methylimidazole, 2-phenylimidazole or1-cyanoethyl-2-phenylimidazole.
 12. The process according to claim 4wherein the catalyst is 2-ethyl-4-methylimidazole, 2-phenylimidazole or1-cyanoethyl-2-phenylimidazole.
 13. The process according to claim 9wherein the catalyst is 2-ethyl-4-methylimidazole, 2-phenylimidazole or1-cyanoethyl-2-phenylimidazole.
 14. The process according to claim 1wherein the filler is a mineral filler or a ceramic filler.
 15. Theprocess according to claim 14 wherein the filler is fused silica oraluminum oxide.
 16. The process according to claim 1 wherein atwin-screw extruder is used as the continuous reactor, wherein the ratioof screw length to outside screw diameter is from 20 to
 50. 17. Theprocess according to claim 16 wherein the reactor includes shaftsconsisting of conveying screw elements or of conveying screw elementsand kneading elements, and wherein the residence time of the materialbeing extruded at a screw speed of >10 rpm and with minimum axialbackflow, is <5 minutes.